1. Field of the Invention
This invention relates to a hand-held dispenser for dispensing liquid or semi-liquid material from a collapsible tube.
2. Description of the Related Art
Collapsible tubes are widely known by the public for use as containers for toothpaste and household adhesives. Collapsible tubes are also popular containers for caulk, sealants and other liquid or semi-liquid materials used in construction, vehicle manufacturing and other industries. Collapsible tubes are favored as containers for many materials such as "instant-setting" adhesives because the tube is relatively inexpensive and provides a better initial seal from the atmosphere than, for example, caulking-gun type containers. Once the tube is emptied, the tube can be conveniently disposed of without clean-up as might be necessary with other dispensing systems where the material is transferred from a bulk container to a second container for dispensing.
Hand-held dispensers for collapsible tubes have sometimes used controlled air pressure within a housing containing the tube in order to squeeze the tube and dispense material to a desired location. Examples of hand-held pressurized air dispensers for collapsible tubes are shown for example in U.S. Pat. Nos. 3,871,553 and 3,938,709, both of which illustrate a dispenser having an internal chamber, a rear opening for admitting a tube into the chamber, and a somewhat smaller front opening for receiving a nozzle of the collapsible tube. In the devices shown in the above-mentioned patents, the operator controls the pressure of air in the chamber so that collapsing of the tube is regulated to some degree.
However, air is compressible, and it is sometimes difficult to control the air pressure in a chamber in order to squeeze a tube in such a fashion that only a certain amount of material at a desired flow rate is extruded from the tube. Another problem that may occur is known as run-on, where material dribbles or oozes from the nozzle after an intended end of a dispensing operation, a particular problem when the tube is made of a material that does not have significant shape memory. Problems of imprecise control and run-on are a significant nuisance with workpieces such as small electronic circuit boards where little space is available to hold excess material.